1. Field of the Invention
The present invention relates generally to the field of medicine and, more specifically, to the field of treating cardiovascular disease.
2. Background Information
Coronary artery disease is the most common, serious, chronic, life-threatening illness in the United States, causing more deaths, disability and econonomic loss than many other illnesses. Atherosclerosis is a major cause of myocardial ischemia, which results in a lack of oxygen due to an imbalance between oxygen supply and demand.
Atherosclerosis is responsible for the majority of cases of myocardial and cerebral infarction and thus represents the principal cause of death in the United States and western Europe. Atherosclerosis refers to the thickened and hardened lesions of the medium and large muscular and elastic arteries. Atherosclerosis is characterized by lipid-rich lesions that occur within the innermost layer of the artery, the intima. The lesions are usually eccentric and, if they become sufficiently large, can occlude the artery and thus the vascular supply to a tissue or organ, resulting in ischemia or necrosis. If this occurs, it often leads to the characteristic clinical sequelae of myocardial infarction, cerebral infarction, gangrene of the extremities, or sudden cardiac death.
The two principal forms of atherosclerosis are the early lesion, or fatty streak, and the advanced lesion, or fibrous plaque, which can become an advanced complicated lesion. The fatty streak is the most common and ubiquitous lesion of atherosclerosis. The lesions of atherosclerosis are confined principally to the intima. Initially, the fatty streak appears to contain two cell types, foam cells that consist of macrophages filled with lipids, and T lymphocytes. The macrophages are derived from blood-borne monocytes that are chemotactically attracted into the artery wall, where they develop into foam cells.
The fibrous plaque is also located in the intima and characteristically leads to the eccentric thickening of the artery that often results in an occluded lumen. The fibrous plaque is typically covered at its luminal aspect by a thickened cap of dense connective tissue containing a special form of flattened, pancake-shaped smooth muscle cell that has formed the dense collagenous matrix in which it is embedded. Beneath this cap, the lesion is highly cellular and contains large numbers of smooth muscle cells, some of which are full of lipid droplets. It also contains numerous macrphages, many of which take the form of foam cells, together with variable numbers of T lymphocytes. These collections of cells usually overlie a deeper area of necrotic foam cells and debris. This necrotic area sometimes becomes calcified and often contains cholesterol crystals.
Risk factors for atherosclerosis include hypercholesterolemia, hypertension, cigarette smoking, obesity, as well as other factors. Atherosclerotic disease can be treated by life-style changes such as modified diet, exercise and stopping cigarette smoking. A variety of drug regimens can also be used, for example, to reduce cholesterol levels or blood pressure.
Despite the availability of drug and life-style interventions that modify risk factors for the development of atherosclerosis, a large number of individuals develop ischemic heart disease. Many patients who develop ischemic heart disease are improved by coronary revascularization procedures such as coronary artery bypass grafting or angioplasty. In the case of coronary artery bypass grafting, the method is effective in relieving symptoms, can achieve complete revascularization and is widely applicable. Disadvantages of coronary bypass surgery include high cost, increased risk of the need to repeat the procedure due to late graft closure, and morbidity.
Angioplasty provides the advantage of being less invasive, requiring a shorter hospital stay, having lower initial costs, and being effective in relieving symptoms. Disadvantages of angioplasty include restenosis, high incidence of incomplete revascularization, and uncertain long-term outcome. Restenosis occurs in about 30–45% of cases within 6 months of the angioplastic procedure.
More than 400,000 angioplastic procedures are performed in the United States each year. Therefore, the high recurrence of stenosis (restenosis) means that a significant number of patients must undergo follow up procedures, including repeated angioplasty.
Thus, there exists a need to improve the outcome of invasive vascular procedures such as angioplasty. The present invention satisfies this need, and provides related advantages as well.